This invention relates generally to the hydrocleaning of a pipeline or the like to remove coatings and miscellaneous contaminants from the pipeline exterior surface.
Oil and gas transmission pipelines of large diameter (12"-60-) are usually coated and then buried before being used for transportation of fluids. The coatings serve to reduce corrosion caused by the various soils encountered.
The coating may be put on the pipe after it has been welded together in sections and before the welded line is buried. The coating process is usually continuous. In an alternate case the pipe sections are delivered to the site already shop coated except for 1'-2' on each end. Then another coating is applied to cover the previously uncoated ends of each section after the welding and before the whole line is buried.
In recent developments several pipeline operators have experienced underground failures of old coatings. These failures comprise disbondments between parts of the coating and the pipe which have occurred for various reasons. Despite the continuous use of cathodic protection the sites are conducive to pitting corrosion and to stress corrosion cracking (SCC) and, in severe cases, pipe failures have occurred under pressure. The situation has prompted many operators to initiate coating rehabilitation projects. Almost all SCC cases have been encountered in lines in the ground for 10 years or more.
For rehabilitation, the coated line must be uncovered, pulled up out of the ground and suspended, thoroughly cleaned of all of the old coating, inspected, re-coated and re-buried.
One most recent project in Canada was a program to rehabilitate many miles of a 36" OD gas pipeline. The equipment that has been used to date to remove the old coatings has not performed well enough to meet the operator's time schedule. The technique employs a self-propelled device fitted around the pipe which continuously cuts, scrapes and brushes the coating with steel knives and brushes. This method does remove some of the oldest coal tar coatings fairly well but performs unsatisfactorily on the polyethylene tape layered coatings of more recent vintage. The process leaves adhesive and tape residue and the knives can seriously damage the pipe surface. This machine has been around for approximately 20 years.
A general objective of the invention is to provide method and apparatus for the hydrocleaning of a pipeline, to effect pipe coating removal to thereby clean the pipe surface prior to grit blasting or alternatively to effect cleaning of the pipe surface to "near white" or "white" condition in preparation for subsequent re-coating.
A more specific objective is to provide an ultra high pressure water jetting system to effect removal of pipeline coatings and to achieve cleaning of the pipe surface in a continuous one-pass operation, which cleaning operation would precede the surface preparation (grit or shot blast) and re-coating processes.
A further objective is to provide a hydrocleaning system capable of replacing conventional coating removal systems utilizing knives and/or brushes and the like and which system in particular is capable of removing coatings of plastic tapes made of polyethylene, fusion bond epoxies and the like.
Some additional specific objectives are to provide:
(1) a self-propelled cleaning unit which can be remotely controlled for optimization of cleaning rates and personnel safety. PA1 (2) adjustable cleaning means to permit of pipelines or pipes ranging in size from 12" OD to about 60" OD. PA1 (3) a hydrocleaning method that does not require spinning of the pipe as it is being cleaned. PA1 (4) a hydrocleaning system that can use the pipeline itself as a "monorail" for linear travel therealong and while the pipeline is "in situ" or out of the ground as desired. PA1 (5) a hydrocleaning system that is capable of removing a wide variety of coatings commonly used on pipelines while containing the removed coatings and permitting their disposal in a safe environmentally acceptable fashion. PA1 (6) a hydrocleaning system that is capable of working continuously in conjunction with and ahead of a pipeline re-coating machine.
Accordingly, in one aspect, the invention provides apparatus for the hydrocleaning of the exterior surface of a pipeline or the like including a frame adapted to surround a portion of a pipeline and defining a longitudinal passage through which, in use, the pipeline extends. A plurality of liquid jet nozzle means are mounted to said frame in spaced apart relation so as to surround, in use, said pipeline in circumferentially spaced apart relationship to one another and with each said nozzle means in spaced relation to the pipeline exterior surface. Means for supplying high pressure liquid to said nozzle means to cause liquid jets to be emitted from said nozzle means are provided. The nozzle means and the frame are adapted to move relative to the pipeline surface when in operation such that (i) the liquid jets from said nozzle means impinge on the pipeline surface along prescribed paths located in an annular region extending around substantially the full circumferential extent of the pipeline and (ii) the annular region travels longitudinally relative to the pipeline to effect cleaning of the pipeline exterior surface.
The nozzle means are in another aspect of the invention mounted to said frame for rotation about rotation axes which, in use, are generally normal to the pipeline exterior surface.
Means on said frame may be provided for supporting the latter on said pipeline and in spaced relation to the pipeline surface and for moving the frame longitudinally of the pipeline.
Preferably, the means for supporting and moving the frame comprise wheel means mounted to said frame and adapted to engage the pipeline surface at circumferentially spaced apart intervals, and drive means for rotating said wheels to advance the frame along the pipeline.
Another major aspect of the invention concerns the fact that in many cases pipeline operators would prefer to remove the old coating of their pipeline "in situ". This means that they would not cut the line after excavating and would not lift it above ground. Instead they would simply excavate beside and beneath the line and then, with oil and/or other liquid products still inside the line, would remove and replace the old coating. For safety, however, the internal line pressure would be considerably reduced. The line would be supported ahead and behind the moving machine by wooden blocks called "skids".
In order to provide for "in situ" hydrocleaning, the invention in a further important aspect provides a machine that can be "opened up" and fitted down over the pipeline and then "closed" so that the spray nozzles are all reasonably evenly arranged circumferentially around the pipe's surface and radially spaced therefrom. The machine can easily be removed from the line by reversing the actions above described.
The nozzle means in a further aspect of the invention are arranged such that the prescribed paths along which said liquid jets impinge on the pipeline surface form a series of closely spaced overlapping convolutions. The nozzle means comprise rotary jet heads mounted to said frame that allow for the nozzles' rotation about said rotation axes and the nozzle means are preferably adjustably mounted to the frame to permit their radial locations to be varied to accommodate a variety of pipeline diameters and to provide a desired spacing between the pipeline surface and liquid jet emitting portions of said nozzle means.
Rotation of the rotary jet heads above the surface of the large steel pipes used for pipelines requires maintaining a consistent safe jet head to pipe spacing despite variations in pipe diameter (these can be up to 1% of diameter), out of roundness, dents and wrinkles in the pipe's surface. If not, serious damage could result. Hence, in a further aspect of the invention, a fixed clearance is achieved by suspending the rotary jet head assembly from the frame by means of a special hinged arrangement, typically a four bar linkage, that ensures that the jet head can move in a radial direction but will always stay in a constant alignment with respect to the pipe's axis. At the same time a hydraulic cylinder/accumulator system (well known per se in the art) maintains a compression on a guide wheel having a screw jack height adjustment which fixes the head to pipe clearance. Thus the rotating jet head will maintain a fixed relationship to the pipe's outer surface despite diametral dimensional variations and surface deformations that may be encountered.
The nozzle means typically comprise rotary jet heads having one or more nozzles. In the case of a single nozzle (i.e. producing a single water jet) if the nozzle arms are relatively long and their rotation speed is high then the rotating member needs to be dynamically balanced to avoid serious vibrations. The answer is to equip the head with two identical arms except that one of the two ends is plugged off with a blanked or plugged nozzle. Rotary jet heads with an odd number of operating jets greater than one would require a number of blanks inserted while maintaining geometric symmetry for ease of balancing the rotating member.
The means for supplying high pressure liquid preferably comprises a high pressure pump means and a prime mover, water storage means and flexible hose means connected between said pump means and said nozzle means to supply the high pressure liquid thereto. The high pressure pump, prime mover and water storage means are preferably mounted to means capable of travelling alongside the pipeline. The apparatus may also include means connected to said frame and supported from the ground for preventing rotation of said frame around the pipeline during the relative movement between the frame and the pipeline surface.
Many pipeline operators have lines that were coated in the past with materials which are environmentally unacceptable, for one reason or another. Some coatings contain varying percentages of materials such as asbestos, fiberglass and bituminous materials. In some instances these materials cannot be simply buried with the line or dumped on the ground after they have removed them with the water jets. They must be disposed in an approved disposal site.
Accordingly, in a further aspect of the invention, provision is made for containment and disposal of such waste material produced by the hydrocleaning process. Preferably, the whole machine is enclosed with a canopy of a suitable light material and a catchment sump is located beneath the machine. From the sump the slurry of water and coating debris can be pumped to disposal tankers using suitable vacuum pumps. In some cases the possibility exists for separating most of the water and cleaning it of solids and re-using it for hydrocleaning the pipeline.
Another feature of the invention concerns the fact that a pipeline operator has to excavate earth so as to expose the total circumference of the line with sufficient annular clearance beside and beneath the line for subsequent machines to pass. However, with some oil or gas products in the line under pressure, the use of a heavy bucket of a back hoe or the use of ditching scoops on a continuous ditch excavating machine could be dangerous since the pipe might be impacted by such moving equipment. A reasonably safe excavation procedure leaves a substantial amount of earth still to be removed from around the pipe by other safer means.
Accordingly, another feature of the invention provides means for washing away the residual earth from around the pipe. The hydrocleaning machine is made to function as an earth excavator by providing jet heads arranged so that the water jets are directed generally in a direction ahead of the machine to thus wash the earth residue from the line. Each jet head is rotated so as to achieve total coverage of the surface to be washed.
A further aspect of the invention provides a method for the hydrocleaning of the exterior surface of a pipeline or the like. The method includes positioning a plurality of liquid jet nozzle means around a pipeline in circumferentially spaced apart relation to one another and in preselected spaced relation to the pipeline exterior surface and supplying high pressure liquid to said nozzle means to cause emission of liquid jets from said nozzle means. These liquid jets are caused to impinge on the pipeline exterior surface along prescribed paths located in an annular region extending around substantially the full circumferential extent of the pipeline as said annular region of impingement moves relative to said pipeline longitudinally thereof to effect cleaning of the pipeline exterior surface.
The nozzle means in a further aspect of the invention rotates about axes normal to said pipeline surface with said liquid jets being emitted from said nozzle means in radially spaced relation to said rotation axes. The prescribed paths along which said liquid jets impinge on the pipeline surface form a series of closely spaced overlapping convolutions.
Further features and advantages of the invention will become apparent from the following description of preferred embodiments of same, reference being had to the accompanying drawings.